Various techniques exist for estimating the position and velocity of a moving transmitter based on passive measurements made by a moving sensor. Some of these techniques rely on combining measurements from several types of sensors, e.g., optical, electromagnetic, and acoustic. Some also require a plurality of platforms, each equipped with its own sensor or set of sensors. Such limitations restrict the applicability of these techniques. The prior art also includes a series of three techniques that allow the estimation of the position and velocity of a moving transmitter provided that the transmitter is traveling linearly at a constant velocity and that the sensor's motion is constrained to match some a priori trajectory. U.S. Pat. No. 4,179,697 discloses a method applicable when the sensor is constrained to be moving along a known curved trajectory at a constant speed. U.S. Pat. No. 4,558,323 discloses a method applicable when the sensor is constrained to be moving along a linear trajectory at a non-constant speed. U.S. Pat. No. 4,613,867 discloses a method applicable when the sensor is constrained to be moving along a linear trajectory at a constant speed. The first two of these methods use passive bearing measurements made while the sensor traverses its constrained trajectory. The third method uses passive frequency measurements and passive bearing measurements made while the sensor traverses its constrained trajectory. Yet another method, as disclosed in U.S. Pat. No. 4,788,548, exploits the curvature of the received signal's wavefront to estimate a moving or stationary transmitter's position; however, it is incapable of estimating the transmitter's velocity.
The present invention provides a method that removes the limitations and constraints of the methods of the prior art.